Performance evaluation of online motion synchronizing systems for patient-specific respiratory movements with helical tomotherapy

Abstract

Background and purpose.The introduction of online motion synchronizing system on helical tomotherapy paves way for robust motion tracking. A recent upgrade launches modifications on both hardware and software of the kV tracking system. An evaluation on the kV subsystems, prior (Version1) and post upgrade (Version2), was performed to compare tracking accuracy by means of fiducial tracking error and resulted root-mean-square (RMS). Impacts influenced by various patient-specific breathing pattern regularities and target movements were also investigated to refine motion tracking error estimations upon future selection of possible candidates.Materials and methods.Respiratory patterns from twenty-five lung cases were imported individually into a commercial dynamic platform model. Situating a phantom implanted with gold fiducial markers on the platform, superior-inferior (SI) movements of corresponding targets were simulated. Each case was delivered via an identical treatment plan in Version1 and was repeated in Version2. Motion tracking accuracy, by means of discrepancies between subsystem predicted model and raw data motion recorded in patient CT simulation, was analyzed statistically. Wilcoxon signed ranked test was employed to evaluate the difference in tracking error range between the two versions. Statistical model was fitted to inspect the dependence of internal target movement towards fiducial tracking errors.Results.A small difference of ±1 mm was exhibited in 99% of fiducial tracking errors for all cases experimented under both versions. RMS errors were all below 0.5 mm. Version2 demonstrated a greater extremity in fiducial tracking error (p = 0.04). A positive correlation was depicted between internal target amplitudes and 95% interval of fiducial tracking errors (p < 0.02). Overall, irregular respiratory patterns tended to have greater fiducial tracking errors.Conclusions.The excellent tracking performance in both kV subsystem versions offers motion compensations benefits, yet Version1 outperformed Version2 in fiducial tracking accuracy. It is noticeable that greater magnitude in internal target movement and irregular breathing patterns yield greater tracking error.

Keywords: online motion tracking; radixact; synchrony; tomotherapy.